Removal of lead coatings from metallic articles



Patented Dec. 16, 1930 omen srarss PATENT, OFFICE KIEL IB. BOWMAN, OF MASSILLON, OHIO, ASSIGNOR, BY MESNE ASSIGNMENTS, 'IO RE- PUBLIC STEEL CORPORATION, OF YOUNGSTOWN, OHIO, A CORPORATION OF'NEW JERSEY REMOVAL LEAD COATINGS FROM METALLIC ARTICLES No Drawing.

This invention relates in general to the removal of metallic coatings from coated metallic articles and more particularly to a novel method of removing or separating the lead coating from lead coated cold drawn steel rods or tubes.

In the process of cold drawing steel rods and tubes, the rods or tubes are usually coated with grease to facilitate drawing them.

through the dies. The drawing grease is not only inconvenient to handle but its use makes it necessary to anneal the tube or rod frequently between passes through the drawing dies, and the grease must be removed before each annealing.

To overcome these objectionable features,

a method has recently come into general use,

in which the hot rolled pickled tubes or rods are coated with lead and then put through the drawing dies. The use of a lead coating, in-

stead of drawing grease, dispenses with the necessity of annealing the tubes or rods between passes, but has the disadvantage that the lead coating must be removed after the final pass so that the tubes or rods may be annealed, because the lead coating would otherwise penetrate the steel surface and cause a separation of the crystals at their rain boundaries. In removing this lead coat- 39 mg the tube or rod surface must be kept smooth and must not be attacked appreciably by the reagents used in the removal treatment. 1

In order to realize the advantages of lead 5 coating, and at the same time obviate the aforesaid disadvantages, I have devised a method of removing the lead coating which is highly eificacious and is simple, practical and economical as well.

40 I take the lead coated cold drawn steel rods or tubes-and place them in a bath of molten or fused-sodium nitrate or other suitable alkaline oxidizing agent, which will not appreciably attack the base metal, such as sodi-' 46 um nitrite, sodium peroxide, sodium chlorate,

Application filed October 8, 1929. Serial No. 898,276.

and the corresponding potassium compounds. the bath being maintained at a temperature varying from the fusing point of the oxidizing agent up to any temperature which will not cause thenoxidizing agent to attack the base metal. In practice, the desired temperature may vary from about 500 F. to about 1000- F. This treatment converts the lead coating to lead oxides, which adhere to a varying extent to the base metal.

I The tubes or rods are then removed from the aforesaid bath and are quenched in cold water to remove any of the oxides which do not adhere to the base metal, as the oxides which can be thus removed, need not be later removed by the pickling acid.

They are then pickled in hydrochloric acid or any acid which dissolves lead oxides, such as nitric acid, sulphuric acid, acetic acid, phosphoric acid, ete. Hydrochloric acid is preferred because it is relatively inexpensive and does not attack the base metal to an appreciable extent. The higher the temperature of the pickling acid, the more rapidly the lead oxides are dissolved, and in practice temperatures up to the boiling point of the acid may be employed. The acid may be used in any desired concentration up to 100% of commercial acid by Volume, and may contain an inhibiting agent, such as thio-urea, for the purposeof preventing the base metal from being attacked by the acid.

In the following table, the results of a series of experiments are given, showing the efiects of the lead removal treatment according to my novel treatment and according to one other lead removal treatment. The samples were all cut from the same piece of lead coated seamless tubing, which had been cold drawn to size, and were all of approximately the same length.

Samples Nos. 1, 2 and 3 were treated in sodium nitrate (NaNo at 780 F. for five minutes, quenched in cold Water, and then pickled for five minutes in a solution containing 50% hydrochloric acid (H01) by volume, at a temperature of 150 F., the solutlon con- ,taining a small quantity of thio-urea.

Sample No. 4 was pickled in a solution containing 5%v nitric acid (HNO by volume until the lead was removed.

\ These results clearly show that the treatment, as set forth herein, is highly advantageons from a commercial standpoint, in that it results in removal of the lead coating and at the same time leavesthe ferrous base of the article clean and smooth.

It will be understood that the process may also be used for removing lead coatings from articles having a non-ferrous base.

Without further description, it is thought that the features and advantages of the invention will be readily apparent to those skilled in the art, and it will of course be understood that changes in the proportions, temperatures and other details of the process may be resorted to Without departing from the scope of the appended claims.

Claims:

1. The method of removing the lead coating from lead coated articles, which consists in treating the articles with an agent which oxidizes the lead coating and then removing the oxidized lead coating by means of an acid.

2. The method of removing the lead coating from lead coated ferrous base articles, which consists in treating the articles with an agent which oxidizes the lead coating and then removing the oxidized lead coating by means of an acid.

3. The method of removing the lead coat- 111g from lead coated articles, which consists in treating the articles with sodium nitrate to oxidize the lead coating and then removing the oxidized lead coating with hydrochloric acid. Y 4. The method of removing the lead coat- 1ng from lead coated ferrous base articles, which consists in treating the articles with sodium nitrate to oxidize the lead coating and then removing the oxidized lead coating with hydrochloric acid.

5. The method of removing the lead coatng from lead coated articles, which consists 1n oxidizing the lead coating and then re movin the oxidized lead coating. 1

6. T e method of removing the lead from lead coated ferrous base articles, which consists in oxidizing the lead coating and then removing the oxidized lead coating.

7 The method of removing the lead coat I ing from lead coated articles, which consists 9. The method of removing the lead coating from lead coated articles, which includes the step of oxidizing the lead coating to facilitate removal thereof.

10. The method of removing the lead coating from lead coated ferrous base articles, 7

which includes the step of oxidizing the lead coating to facilitate removal thereof.

In testimony whereof I aflix my signature.

KIEL B, BOWMAN. 

